Conventional processors for developing exposed X-ray film have been known to use an optical scanner system to determine the length and width of the film before it is transported through the processor. Typically, this size information is used to adjust the input of fresh chemicals into the processor, as well as to sort the exposed film according to size.
One processor is known to use an array of infrared transmitting diodes to scan the film. Located opposite from the transmitting diodes are a lesser number of infrared detecting diodes. When the film is transmitted between the transmitting and detecting arrays, some of the infrared light is blocked from reaching the detector diodes. This information can be used to adjust the replenishment rate of chemicals into the processor.
A problem in using an infrared measurement system is that some of the newer X-ray films exhibit sensitivity in the infrared region. Thus when these films are exposed to infrared energy, the film becomes "fogged" thereby obscuring the developed image.
Conventionally, a number of detection systems have been disclosed. For example, in U.S. Pat. No. 3,603,680 by Barton, there is disclosed an ultrasonic paper detection system which utilizes a plurality of transmitter and receiver transducers to generate timing signals when the sonic path therebetween is interrupted by the travel of paper.
Kanda et al, in U.S. Pat. No. 4,511,998, discloses an acoustic imaging instrument which includes opposing arrays of acoustic transducer elements and acoustic detecting elements.
In U.S. Pat. No. 4,513,404 by Huggins an acoustic system for detecting the presence or absence of paper includes a receiver which detects a change in the acoustic impedance of a receiving port when the paper is absent or in close proximity to the port.
Furthermore, Miyamoto in U.S. Pat. No. 4,620,781, discloses an image processing system which includes a photosensor for detecting the size of an original document.
And also, in U.S. Pat. No. 4,494,841 by Marcus, which is assiged to the assignee of the present invention, there is disclosed an acoustic position sensing apparatus which is utilized to sense the position of an object relative to a sensing port in an acoustic resonator.